Protective barrier

ABSTRACT

A protection product has thermal and acoustic barrier characteristics such that it satisfies the requirements of the standard 14 CFR, part 25 issued by the Federal Aviation Administration. The product is designed to be applied along metallic and composite structures, such as aircraft cockpits, boat hulls or the outside structures of trains or of other means of transport. The product is essentially in the form of a “mat” consisting of one or several fiber layers, preferably glass fibers, enclosed in a sheath. The sheath generally comprises at least one first support, preferably made of an organic material having sealing and anti-condensation properties, and an impregnated mica paper. The mica paper preferably has a weight per unit area of less than 50 g/m 2  and comprises flakes of mica with a form factor greater than 1000.

RELATED APPLICATIONS

This is the U.S. National Phase under 35 U.S.C. § 371 of InternationalApplication No. PCT/BE01/00107 filed on Jun. 21, 2001, designating theUnited States and published in French on Dec. 27, 2001 as publicationNo. WO 01/98434, which claims priority to European Application Nos.00870138.5, filed Jun. 21, 2000 and 00870270.6, filed Nov. 13, 2000.

OBJECT OF THE INVENTION

The present invention relates to a fire protective barrier designed tobe applied along the inside of metallic or composite structures, such asaircraft cockpits, boat hulls or other means of transport.

The present invention likewise relates to vehicles such as aircraft,boats, trains etc. that use a fire protective barrier of this kind.

TECHNOLOGICAL BACKGROUND

Metallic and composite structures such as aircraft cockpits or boathulls are usually covered on the inside with protection having thermaland acoustic barrier characteristics in order to insulate the inside ofthe cockpit or of the hull from the outside environment.

To this end, proposals have been made for protection systems, which areusually in the form of a mat consisting essentially of one or severallayers of glass fibres enclosed in a sheath. This sheath can be producedfrom any type of material. Preferably, it is a film made of an organicmaterial, such as polyester, polyimide etc. having at least hydrophobiccharacteristics and acting in certain cases as a water-tight barrier. Byway of example, one may mention as a material used to produce the sheathaluminised or unaluminised mylar®, tedlar®, which is produced in a filmof PVF, kapton®, which is a film produced from polyimide (registeredtrademarks of Dupont), or other coverings, such as polyester orpolyamide films, such as textril®, which is a polyester film reinforcedwith polyethylene fibres made by the Jehier company. These films formingthe sheath must be produced from materials that allow the customarytextile treatments: stitching, bonding, welding etc. and have mechanicalcharacteristics such as resistance to tearing etc.

On the other hand, reflecting a concern to minimise weight, the densityof these various materials should be as low as possible while at thesame time allowing superior mechanical characteristics to be achieved.The weight per unit area of this type of protection is preferably lessthan 100 g/m².

It is absolutely essential to protect as far as possible the passengersinside an aircraft from the risk of ignition of the fuel generallycoming from external engines. Indeed, when it ignites, this fuel, suchas kerosene, reaches temperatures well above 1000° C. Due to this fact,it is advisable to protect the elements of metallic and compositestructures forming aircraft cockpits, boat hulls, outside structures oftrains etc.

To this end, the authorities and, in particular, the FAA (FederalAviation Administration) have established relatively strict fireprotection standards. However, the standards to which aircraftmanufacturers have to conform are continually evolving and are becomingever more stringent, reflecting a concern of increased safety oftravellers.

The fireproofing characteristics of the protection systems describedabove, which belong to the prior art, are nowadays found to beinadequate. The transport department of the FAA has therefore attemptedto publish test criteria appropriate to the new requirements. Inparticular, the characteristics of resistance to the “burn-through test”and the “inflammability test” were redefined in September 2000 instandard 14 CFR, part 25 et al.

In particular, the “burn-through” test consists in subjecting the mat offibres and its sheath to the flame of a burner. The said burner suppliesan impinging flame at a temperature of around 1150° C. The sample isthus subjected to a heat flux of 149 kW/m². The product concerned willsatisfy the requirements of the FAA if it succeeds in resistingpenetration by the said flame for 4 minutes and if the heat fluxproduced by the sample is less than 23 kW/m², measured at a distance of30.5 cm (12 inches) from the impingement surface.

The inflammability test (ASTM-E 648), which consists in subjecting asample measuring 1000 mm in length and 250 mm in width to a radiantpanel sloping at 30° in front of the sample and in the presence of apilot flame. The radiant panel produces a heat flux of 18 kW/m² andignition is effected by means of a pilot flame. The criteria for passingthe test are the absence of flames within a radius of 51 mm around thepoint of application and the absence of post-combustion after extinctionof the pilot flame for a specific test period.

Aircraft manufacturers have likewise defined certain mechanicalspecifications, such as flexibility and tensile strength, and theirvariation, obtained as a result of standardised conditioning or ageingof the samples.

On the other hand, the prior art, in particular the documentEP-A-0370337, has disclosed the use of an impregnated mica paper,possibly bonded to a support based on woven or nonwoven glass fibres,aramid fibres, carbon fibres or some other type, such as a fireproofingcovering with a low rate of heat release for construction elements inapplications subject to relatively stringent standards in this matter,such as the aeronautical industry, the automotive industry, interiordecoration etc.

Although this type of use for mica paper initially satisfied thestandards in force in the 1980s (ATS 10 333-001, directive FAR 25—OSUchamber), this type of covering does not satisfy the new safetystandards, such as those defined above.

It is likewise known, in particular from the documents EP-A-0949367,FR-A-3 884 337, EP-A-0406467 and U.S. Pat. No. 4,514,466, that mica and,in particular, mica paper is a good electrical insulator and has goodheat resistance. Nevertheless, these documents do not mention the use ofmica for a fire protective barrier applied along a metallic or compositestructure such as an aircraft cockpit, a boat hull or the outsidestructure of a train etc.

It will furthermore be noted that, in all the prior-art applications,the conventional mica paper has a weight per unit area close to 100g/m².

AIMS OF THE INVENTION

The present invention aims to propose a protection product which has atleast the same acoustic and thermal insulation characteristics as theprior-art products and equivalent behaviour as an anti-condensationbarrier.

In particular, the present invention aims to propose a product for useas a fireproofing barrier which satisfies the new requirements of theFAA, that is to say which meets the standards defined by regulation 14CFR, part 25.

More particularly, the present invention aims to propose a protectionproduct which has satisfactory behaviour in the “burn-through” test andin the inflammability test, which are defined in this regulation.

Moreover, the present invention aims to allow solutions which increasethe ultimate weight of the material as little as possible, that is tosay which allow the provision of a sheath that has a total weight perunit area of less than 100 g/m².

MAIN CHARACTERISTIC ELEMENTS OF THE INVENTION

The present invention relates to a protection product having thermal andacoustic barrier characteristics designed to be applied along metallicand composite structures, such as aircraft cockpits, boat hulls or trainstructures, essentially in the form of a mat consisting of one orseveral fibre layers, preferably glass fibres, enclosed in a sheath,characterised in that the sheath comprises at least one first supporthaving moisture-tightness and anticondensation characteristics andpreferably made of an organic material, and an impregnated mica paper.

According to a first embodiment, the sheath comprising the mica paperand the first support is produced in the form of a single layer, inwhich the mica paper adheres directly to the support.

According to a second embodiment, the sheath is in the form of amulti-layer complex comprising, on the one hand, the support having therequired moisture-tightness and anticondensation characteristics and, onthe other hand, a mica paper, possibly adhering to a second, dedicatedsupport.

The mica paper is advantageously laminated to a second, dedicatedsupport, preferably to a fabric support such as glass silk or a film.

The first support is advantageously a film or a fabric.

The weight of the mica paper per unit area is preferably less than 50g/m² and preferably less than 30 g/m². It is particularly preferred thatthe weight of the mica paper per unit area is less than 25 g/m² andpreferably less than 20 g/m².

Finally, the present invention relates to a metallic or compositestructure such as an aircraft cockpit, a boat hull or the outsidestructure of a train, to which the product according to the invention isapplied.

It is particularly surprising that the use of such thin mica paper, thatis to say with a weight per unit area of less than 50 g/m², hascompletely satisfactory characteristics, complying with theanti-inflammability and “burn-through” tests.

It is highly probable that the reason for this is that, to produce suchpapers, it is necessary to use a pulp of mica flakes of which 90% byvolume will be less than 800 μm in size. Moreover, these flakes willpreferably have a large form factor (that is to say diameter divided bythickness), and preferably a form factor greater than 1000. It should benoted that the mica paper will be produced by customary techniquesdescribed in the prior art and impregnated with different types ofresin, e.g. silicone.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in greater detail with referenceto the examples which follow. In these examples, a “mica paper” producedby conventional techniques is used in each case.

The term “mica paper” is intended to mean a sheet produced by the usualpapermaking techniques, which comprises 100% mica in the form ofdirectional flakes. The flakes are usually either of the phlogopite orcalcined or uncalcined muscovite type, or are in the form of a mixtureof the two, or of the fluorophlogopite type, when synthetic mica isused.

The general technique consists in reducing “scraps” of mica to the stateof flakes, the “scraps” being the physical form in which mica ore isextracted from mines. This can be achieved, for example, by mechanicaldisintegration with water and processing of the pulp thus obtained on amachine similar to papermaking machines in order to make a mica paper.Currently, there are several types of mica paper on the market. Thesedepend essentially on the nature of the ore. Muscovite mica papersconsisting entirely of calcined or uncalcined muscovite mica ore,phlogopite mica paper consisting entirely of phlogopite mica ore andmica papers produced from a mixture of different ores are known. Incertain cases, vermiculite is furthermore used, being added to othermaterials to make mica paper.

The use of synthetic mica to create a mica paper is also known.

This mica paper is used as a primary material for the manufacture oftapes, sheets, laminates (micanite). To do this, the mica paper isusually impregnated with organic binders (resins) or inorganic bindersand/or bonded to a mechanically strong flexible support in order toconfer the desired physical properties on the end product.

The level of impregnation of mica papers with organic binders and, inparticular, with silicone resins, is usually between 5 and 25%.

The originality of the mica paper used according to the presentinvention resides in the fact that its weight per unit area isrelatively low and preferably less than 50 g/m².

On the other hand, a glass fibre felt will be produced in a conventionalmanner and wrapped in a sheath consisting of at least one textilesupport and a mica paper according to the present invention. The sheathis referred to below as the finished product.

According to a first embodiment, the said finished product can be in amulti-layer form, that is to say that, in a conventional manner, itcomprises a film of organic material having hydrophobic characteristicsand acting as a water-tight and vapour-tight barrier, and a mica paper,possibly attached to a dedicated support.

According to another embodiment, the said finished product can be in asingle-layer form and consist of a mica paper laminated directly onto afilm having the required hydrophobic characteristics.

EXAMPLE 1

A finished product intended for the production of the sheath isproduced, comprising a mica paper, a textile support and a resin. Tothis end, the following constituents are used:

-   -   a muscovite mica paper with a weight per unit area of 25 g/m²,    -   a glass fabric with a weight per unit area of 24 g/m² formed by        26 warp yarns/cm and 15 weft yarns/cm, the titer of the yarns        being 5.5 tex in both the warp and weft yarns, and    -   a silicone resin of the phenylmethyl silicone type, such as the        resin D.C. 805 from the Dow Corning company.

The mica paper used consists of flakes of muscovite mica and is definedby the following particle distribution: 90% by volume are less than 800μm in size and 10% by volume are less than 80 μm in size. Moreover,their form factor will be greater than 1000. The characteristics of themica paper are as follows:

-   -   weight per unit area: 25 g/m²    -   thickness: 0.016 mm    -   tensile strength: 4 N/cm    -   air porosity: 2200 s/100 cm³    -   oil penetration: 4 s.

To produce the finished product, the glass fibre fabric is impregnatedwith a solution of silicone resin in a toluene solvent medium containing15% dissolved solids. The mica paper is positioned directly on theimpregnated glass fibre fabric. This then absorbs a part of the resin.After evaporation of the solvent in drying ovens provided for thispurpose, the product obtained is rolled up.

In this way, a product consisting of a mica paper laminated onto a glassfibre fabric is produced.

The finished product has the following characteristics:

-   -   total weight: 60 g/m²    -   thickness: 0.059 mm    -   binder content: 20%    -   content of volatiles: 0.2%    -   IEC flexibility: 9 N/m    -   tensile strength: 104 N/cm    -   dielectric strength: 1.08 KV/layer

When the product is subjected to ageing tests corresponding to the EADSAirbus specification, the following results are obtained for materialsintended to meet the specifications of the “burn-through” test afterconditioning at 70° C./98% relative humidity for 500 hours:

-   -   total variation in mass: −0.35%    -   variation in tensile strength: −4%

These values are well below the limits specified by EADS Airbus, whichaccepts a loss of up to 10% in these same properties.

A sample is then subjected to a flame test as described below:

-   -   three samples of the product are conditioned at ambient        temperature and 50% relative humidity for a minimum of 24 hours,    -   a sample measuring 18 cm×18 cm is fixed by its four sides on a        metallic frame with a width of 1 cm, leaving a very slightly        tensioned square surface area of 17 cm×17 cm,    -   the sample is exposed horizontally to the flame of a bunsen        burner with a 1-cm diameter nozzle. The total height of the        flame should be 4 cm and the sample should be placed between the        oxidising and the reducing limit of the flame. This gives a        contact temperature between the flame and the sample of 1100°        C.,    -   the flame is applied to the sample for 10 minutes, and    -   a check is made to ensure that the flame does not pass through        the sample throughout the test.

The same method is employed for all three samples. If none of thesamples as described in this example has been passed through by theflame after 10 minutes of testing, the product fulfils its role of flameprotection perfectly. Even after having extended the tests by 30minutes, the mica paper/glass fibre fabric product is not pierced by theflame.

“Burn-through” tests according to the standard CFR 14, part 25 wereperformed on an insulating mat consisting of two layers of glass fibres,a fire barrier consisting of a sheet of the mica/glass fibre fabricproduct as described above, and a skin of reinforced polyester. Afterthe 4 minutes required for the test, the mica has not been perforated bythe flame and the heat flux levels measured are less than 0.8 W/cm² andhave thus remained well below the maximum value accepted in thespecification of the standard, which is 2 W/cm². The product thuscomplies with standard 14 CFR, part 25.

EXAMPLE 2

A finished product intended to form the sheath consisting of a micapaper, a support, a resin and an adhesive is produced. To this end, useis made of the following materials:

-   -   a muscovite mica paper weighing 20 g/m²,    -   a polyvinylfluoride (PVF) film such as Tedlar® TFM05AL2 from        Dupont de Nemours with a thickness of 12.5μ and a weight of 18        g/m²,    -   a silicone resin of the methyl silicone type, such as the resin        Wacker K from the Wacker company, and    -   a silicone adhesive of the PSA (Pressure Sensitive Adhesive)        type, such as the type DC 280 A from the Dow Corning company.

The mica paper used is of the same type as that used in example 1 andhas the following characteristics:

-   -   weight per unit area: 20 g/m²    -   thickness: 0.014 mm    -   tensile strength: 3 N/cm    -   air porosity: 2000 s/100 cm³    -   oil penetration: 4 s.

To produce the finished product, two steps are performed:

-   1. a step in which the mica paper is reinforced: to do this, the    mica paper is impregnated with a 10% solution of silicone resin K in    a solvent medium, and a mica paper reinforced with 9% of dry    silicone resin is obtained, and-   2. a laminating step, which can be performed in an advantageous    manner by two different techniques:    -   a. the previously reinforced mica paper is coated with a 14%        solution of silicone adhesive 280A in a solvent medium. After        evaporation of the solvent in drying ovens, a PVF film is        laminated onto the mica coated with the silicone adhesive;    -   b. or the PVF film is coated with a 5% solution of silicone        adhesive 280A in a solvent medium. After evaporation of the        solvent in drying ovens, the previously reinforced mica paper is        laminated onto the PVF film coated with the silicone adhesive.

A product made up of a mica paper laminated onto a PVF film is obtainedin this way. The finished product has the following characteristics:

-   -   total weight: 48 g/m²    -   thickness: 0.050 mm    -   binder content: 20%    -   content of volatiles: 0.2%

The results of the ageing tests under humid conditions as specified inthe first example meet the EADS specifications.

In the flame tests as described in example 1, an excellent result islikewise obtained inasmuch as the flame does not pass through the micapaper/Tedlar® film product after the 10 minutes of testing.

EXAMPLE 3

A variant of the product is produced by the same method as thatdescribed in example 2, but replacing the Tedlar® PVF film with a 6-μMylar® polyester film obtained from the Dupont de Nemours company.

The results obtained are comparable to those in the preceding examples.

EXAMPLE 4

Another method of implementation consists in bonding the film onto themica paper by means of spots of adhesive rather than by means of acontinuous film of adhesive. To do this, use is made of well-knowncoating techniques, e.g. coating by means of an engraved cylinder, whichmakes it possible to deposit the adhesive in the form of spots on thesupport.

1. A protection product having thermal and acoustic barrier characteristics such that the product satisfies the requirements of the standard set forth in 14 CFR, part 25 by the Federal Aviation Administration, as amended in September 2000, the product being designed to be applied along metallic and composite structures, said protection product being essentially in the form of a mat comprising one or several fibre layers enclosed in a sheath, wherein the sheath comprises: at least one first support, and an impregnated mica paper, the mica paper having a weight per unit area of less than 30 g/m²and comprising flakes of mica with a form factor greater than 1000, wherein the impregnated mica paper consists essentially of mica and a binder or resin prior to impregnation, and wherein the protection product comprising the impregnated mica paper satisfies said requirements of the standard set forth in 14 CFR, part
 25. 2. The product according to claim 1, wherein the sheath consists of the impregnated mica paper and of the first support adhering directly to the impregnated mica paper.
 3. The product according to claim 1, wherein the sheath is a multi-layer sheath.
 4. The product according to claim 3, wherein a first layer comprises the impregnated mica paper laminated onto a second, dedicated support made of a film or of a fabric, and a second layer is the first support.
 5. The product according to claim 1, wherein the first support is a film.
 6. The product according to claim 1, wherein the first support is a fabric.
 7. The product according to claim 1, wherein the weight of the mica paper per unit area is less than 25 g/m².
 8. The product according to claim 7, wherein the weight of the mica paper unit area is less than 20 g/m².
 9. The product according to claim 1, wherein the metallic and composite structures comprise a structure selected from the group consisting of aircraft cockpits, boat hulls and the outside structures of trains or of other means of transport.
 10. The product according to claim 1, wherein the first support is made of an organic material having sealing and anticondensation properties.
 11. The product according to claim 1, wherein the total weight of the first support and the mica is less than 100 g/m².
 12. The product according to claim 1, wherein the level of impregnation of the impregnated mica paper with the binder or resin is less than 25%.
 13. The product of claim 1, wherein said mica paper comprises mica flakes and 90% by volume of said mica in said mica flakes are less than 800 μm in size.
 14. The product of claim 1, wherein the mica flakes comprise directional flakes.
 15. The product of claim 1, wherein the impregnated mica paper consists essentially of mica and organic binder.
 16. The product of claim 1, wherein the impregnated mica paper consists essentially of mica and silicon resin.
 17. The product of claim 1, wherein the impregnated mica paper consists essentially of mica and inorganic binder.
 18. The product of claim 1, wherein the impregnated mica paper consists essentially of mica and organic resin. 